JPH0229075B2 - TORIPUTOFUANNOSHOSEKIHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for crystallizing tryptophan by adding tryptophan as an aqueous alkaline solution to acetic acid or an aqueous solution of acetic acid.

Tryptophan is one of the essential amino acids and is useful as a nutritional source for the human body or livestock. There is a demand for higher quality tryptophan used in these products.

Manufacturing methods include chemical synthesis methods, enzymatic methods, and fermentation methods. As a method for separating and purifying tryptophan in these manufacturing processes, a method of adding a metal salt to form a double salt of a ceramic body (Japanese Patent Publication No. 1987-
11914), a method using an anion and cation exchange resin (Japanese Patent Laid-Open No. 53-111061), or a method combining an adsorption resin and an ultrafiltration membrane (Japanese Patent Laid-open No. 58-895).

However, since tryptophan has a strong tendency to be adsorbed and desorbed by the resin together with colored substances, complicated steps and operations are required to remove these impurities. Furthermore, impurities such as colored substances are likely to be adsorbed and mixed into tryptophan crystals during crystallization. In order to prevent the contamination of these impurities, there is a method of crystallizing using an organic solvent such as alcohol, but this requires complicated steps such as recovering the solvent.

Since the adsorption affinity of tryptophan is thus large, there is no means to easily remove impurities such as colored substances.

As a result of repeated studies on removing impurities such as colored substances by crystallization, the present inventors discovered that by adding an alkaline aqueous solution of tryptophan to acetic acid or an acetic acid aqueous solution of 30% or more and performing neutralization crystallization. It was found that the quality was significantly improved.

That is, when neutralization crystallization is performed while gradually adding an alkaline aqueous solution of tryptophan to acetic acid or an acetic acid aqueous solution of 30% or more, crystallization and crystal growth of tryptophan gradually progress as the addition progresses. Large shiny hexagonal plate-shaped crystals are obtained.

This is considered to be because the presence of acetic acid at a high concentration suppresses the inhibitory effect of impurities on crystallization and crystal growth during the crystallization and crystal growth process of tryptophan by neutralization crystallization. On the other hand, when neutralization crystallization is performed while gradually adding acetic acid or acetic acid aqueous solution to an alkaline aqueous solution of tryptophan, the resultant crystals are aggregated fine crystals, and many impurities such as colored substances are mixed in.

The alkalis in the alkaline aqueous solution of tryptophan used for neutralization crystallization are NaOH, KOH, LiOH,
Any such as NH ₄ OH may be used as long as the amount is sufficient to dissolve tryptophan.

The tryptophan concentration of the alkaline aqueous tryptophan solution may be about 5 to 40%. If the concentration is higher than this, the viscosity increases and addition crystallization becomes difficult. If the concentration is too low, not only will the amount of crystallization solution increase, resulting in a decrease in the crystallization rate of tryptophan, but also the acetic acid concentration in the crystallization solution will decrease, resulting in poor selection of impurities.

The quality of tryptophan crystals improves as the amount of acetic acid or a 30% or more acetic acid aqueous solution increases, but it is not a good idea since it lowers the crystallization rate and increases the amount of acetic acid consumed. The higher the acetic acid concentration of the acetic acid aqueous solution, the better. If it is lower than 30%, tryptophan becomes fine crystals and its quality deteriorates. In addition, the required amount of acetic acid or its aqueous solution is determined by the amount of alkaline aqueous solution of tryptophan to be added and the alkaline concentration, and as a guideline, the pH at the end of neutralization crystallization is about 2 to 6. good.

The higher the temperature when performing neutralization crystallization by adding an alkaline aqueous solution of tryptophan, the better the crystal quality will be, but if the temperature is too high, the coloring of the crystallization solution tends to increase, so the temperature is preferably 30 to 60°C. Good condition.

The rate of addition is desirably commensurate with crystal growth, and may be approximately 1 to 5 hours.

After neutralization, the product is gradually cooled and crystallized, aged at around room temperature, and then separated.

The method of the present invention can be widely applied to obtaining tryptophan crystals from an aqueous solution containing tryptophan, but is particularly effective in removing impurities derived from fermentation liquids and enzyme reaction liquids containing colored substances.

Examples of this include fermentation liquids, enzyme reaction liquids, their sterilizing solutions, liquids purified from them using ion exchange resins, nonionic resins, ultrafiltration, reverse osmosis, etc. Examples include a mother liquor obtained by crystallizing and separating tryptophan, a solution of its crystals (crude crystals), a synthesis solution, a racemization solution, and a crystallization separation of an optically active substance after splitting the DL form.

In order to remove acetic acid from the obtained crystals, the separated crystals may be washed with water and then dried under reduced pressure at 60 to 80°C for about 10 to 20 hours.

In addition, the method of the present invention can be used to improve the crystal habit of tryptophan obtained by another method if the crystal habit is undesirable, such as aggregated crystals of fine crystals. It is easy to see what can be done.

The following will be described in detail with reference to examples.

Example 1 L-tryptophan fermentation liquid (Japanese Patent Application Laid-open No. 56-92796)
After passing through a strongly acidic cation exchange resin to adsorb L-tryptophan, the resin was thoroughly washed with water and then eluted with a 2N NaOH solution. This eluate was concentrated to obtain an alkaline aqueous solution of tryptophan (tryptophan content 30.3%, PH 12.2).

Take 150g of this concentrated liquid and add it to 50ml of acetic acid for neutralization crystallization at 45°C for 2 hours (completed).
PH3.4) and then cooled to 25°C.

After centrifuging the precipitated crystals, pour 50ml of water onto the crystals.
was sprayed and washed. This was dried under reduced pressure at 70°C to obtain 43.6 g of L-tryptophan crystals (purity 98.8%, yield 94.7%).

The transmittance of this crystal was 77.5% (C=1,
water, 430nm).

Comparative Example 1 150 ml of acetic acid was added to 450 g of the concentrated solution obtained in Example 1, and neutralization crystallization was carried out at 45° C. over 2 hours (finished pH: 3.3). Thereafter, the crystals were cooled to 25°C and centrifuged, and 150 ml of water was sprayed onto the crystals to wash them. This was dried under reduced pressure at 70°C to obtain 133 g of L-tryptophan crystals (purity 97.6%, yield 95.2%).

The transmittance of this crystal was 58.3%. (Measured in the same manner as in Example 1).

Example 2 40g of crystals obtained in Comparative Example 1 and 11g of KOH were added to 200ml of water.
The alkaline aqueous solution of tryptophan that had been dissolved in water was added to 100 ml of a 50% acetic acid aqueous solution for neutralization and crystallization at 30°C for 5 hours, and then at 20°C.
cooled down to.

Centrifuge the precipitated crystals and then transfer 50% onto the crystals.
After spraying 20 ml of acetic acid aqueous solution, washing was further performed with 50 ml of water. This was dried under reduced pressure at 70°C to obtain 36.2 g of L-tryptophan crystals (purity 99.5%, yield 92.3%).

The transmittance of this crystal was 98.1% (Example 1
).

Example 3 L-tryptophan (purity 98.5%, transmittance 87.2
%) and 4 g of NaOH were dissolved in 50 ml of water and heated at 200℃.
Racemization occurred by heating for 2 hours.

This racemized solution was filtered and then added to 20 ml of acetic acid for neutralization and crystallization at 30° C. for 3 hours.

After this, the crystals were washed with 5 ml of acetic acid and further with 10 ml of water, and then dried under reduced pressure at 70°C to obtain 8.3 g of DL-tryptophan crystals (99.3% purity, 83.7% yield).

The transmittance of this crystal was 92.6% (C=1,
1N HCl, 430nm).

Moreover, the specific optical rotation was 0 (C=1, 2N
HCl).

Claims (1)

[Claims] 1. A method for crystallizing tryptophan, which comprises adding an alkaline aqueous solution containing tryptophan to acetic acid or a 30% or more acetic acid aqueous solution.